You can follow a “backpack” travel style with any kind of luggage, so it’s really a matter of personal preference. However, you definitely won’t be doing much “rolling” after you leave the airport on a budget trip in Europe. A roller duffel will not mix with cobble stones, rough sidewalks, curbs and stairs. In many European cities you’ll end up with hotels and hostels with registration desk on “1st” floor — at least 1 flight of steps up from the street, usually without an elevator. Often there’s no elevator (or the elevator is semi-permanently “out of order”) for the 5 floors of steps above that to your room.

Some train stations are “roller friendly” but most have at least a few steps at most entrances and in many cases you will have to go down many steps to the train platforms and then down even more to the subway you need to take to your hostel — then back all the way up to the street.

Load up your duffel with absolutely everything you need to take. Walk around the block twice (a block that has uneven sidewalks and no curb cuts for bicycles and wheel chairs and involves at least some up and down for curbs) then walk immediately up two flights of stairs. If you’re comfortable, take the duffel, but I’m betting you’ll see how useless wheels are and be looking for a backpack.